The present invention relates to a method and apparatus for testing the wrappers of rod-shaped articles (including plain or filter-tipped cigarettes, cigars, cigarillos and cheroots as well as filter rod sections) which constitute or form part of smokers' products. More particularly, the invention relates to a method and apparatus for ascertaining the permeability of wrappers of rod-shaped articles (hereinafter referred to as cigarettes or filter cigarettes) of the type wherein each wrapper includes a portion of greater (predetermined) permeability so that it allows cool atmospheric air to enter the column of tobacco smoke flowing into the smoker's mouth.
It is already known to provide the wrappers of cigarettes with holes or perforations which admit cool atmospheric air into the column of tobacco smoke. The perforated portions of wrappers constitute the so-called climatic zones which are normally adjacent to unlighted ends of the cigarettes. For example, the wrapper of a filter cigarette will be provided with perforations in that portion which surrounds or is closely adjacent to the mouthpiece; this insures that cool atmospheric air will flow into the column of tobacco smoke regardless of the length of non-combusted portion of the tobacco-containing part of the smokers' product. Devices which can be used to perforate selected portions of wrappers of filter cigarettes or the like are disclosed in commonly owned copending applications Ser. Nos. 834,635 filed Sept. 19, 1977 by Heitmann et al., 841,108 filed Oct. 11, 1977 by Wahle et al., and 864,441 filed Dec. 27, 1977 by Luders et al.
Many manufacturers of smokers' products demand that the machines which produce cigarettes, cigars or cigarillos be equipped with perforating devices so as to allow a predetermined quantity of atmospheric air to mix with tobacco smoke which flows toward the mouth. The admixture of atmospheric air to smoke is considered to be desirable because it is believed to reduce the health hazards involved in smoking of tobacco by controlling the amount of nicotine and condensates in the smoke. The packages for cigarettes or other smokers' products must bear information indicating the nicotine content, the tar content and the percentage of certain other ingredients, and the manufacturer is responsible for the accuracy of such information. One of the factors which influence the quantity of nicotine and condensates in the column of tobacco smoke is the quantity of admitted atmospheric air; therefore, it is important to insure that the quantity of admitted air will invariably equal or even slightly exceed a predetermined minimum acceptable value. Consequently, it is necessary to ascertain whether or not the combined cross-sectional area of perforations in the wrappers suffices to guarantee admission of the minimum required quantity of atmospheric air. Furthermore, it is desirable to ascertain the permeability of a finished wrapper (i.e., of the tubular wrapper of a filter cigarette or the like) because this is the only reliable mode of determining the permeability of perforated wrapper portions. For example, certain perforations can be clogged by particles of tobacco or filter material so that, even if the permeability of wrapping material upstream of the wrapping station is clearly adequate, the permeability of perforated portion of the finished wrapper will be too low.
Automatic testing of wrappers of cigarettes or the like for the presence of open seams, holes, frayed ends and other defects is known for nearly two decades. The first successful automatic testing apparatus is disclosed in commonly owned U.S. Pat. No. 3,408,858 to Heinz Kaeding. As a rule, one establishes a pressure differential between the interior and exterior of the wrapper. The pressure differential decreases when the wrapper is defective, e.g., due to the presence of a partly open seam. This is detected by a transducer which furnishes signals to a signal comparing stage (e.g., a threshold circuit) which actuates an ejector when the intensity or another characteristic of the signal is indicative of a defective article. The ejector segregates each defective article from satisfactory articles, for example, by directing streams of compressed air against the ends or sides of defective articles. Presently known testing apparatus are sufficiently accurate to effect the segregation of cigarettes or analogous rod-shaped articles having wrappers which are defective because their permeability exceeds the acceptable permeability by a value corresponding to that which is attributable to the presence of a hole with a diameter of approximately one millimeter. Deviations which are less pronounced cannot be ascertained with a requisite degree of accuracy and reproducibility because the results of tests are influenced by unavoidable factors such as unequal sealing of wrapper ends on successive articles during testing, deviation of density of the tobacco filler from an optimum value, wear upon moving parts of the testing apparatus, clogging of narrow passages in such apparatus by tobacco dust or other foreign matter and/or others. On the other hand, the increased permeability of intentionally perforated portions of wrappers of filter cigarettes or the like is less pronounced than that permeability which is attributable to the presence of a hole with a diameter of one millimeter. Moreover, it is desirable to insure that the permeability of intentionally perforated portions of the wrappers should not deviate from (above or below) an optimum permeability by more than two percent.